Remove six leafovers

readthedocs/core/utils/extend.py

@@ -39,7 +39,7 @@ def __getattr__(cls, attr):  # noqa: pep8 false positive
         return getattr(proxy_class, attr)
 
 
-class SettingsOverrideObject(six.with_metaclass(SettingsOverrideMeta, object)):
+class SettingsOverrideObject(object, metaclass=SettingsOverrideMeta):
 
     """
     Base class for creating class that can be overridden.

readthedocs/rtd_tests/tests/test_views.py

@@ -3,8 +3,8 @@
 from django.contrib.auth.models import User
 from django.test import TestCase
 from django.urls import reverse
-from django.utils.six.moves.urllib.parse import urlsplit
 from django_dynamic_fixture import get, new
+from urllib.parse import urlsplit
 
 from readthedocs.builds.constants import LATEST
 from readthedocs.builds.models import Build